Advice needed for zone damper repair...

I have a home with an attic installed 2 zone HVAC system. The system was installed in December 2003. I have been lucky in that the damper motors have lasted a long time under the hot attic temps. This is in part to the system design and thermostat placement. The house is a one story with a 450 sq ft bonus room as a half story upstairs. The bonus room is the only thing on the second zone. Recently, the upstairs went from being cooled normally to 103 degrees in the afternoon. Being a DIY'er, I read up on the possible issues and narrowed it to a closed zone damper. After a close inspection, I found that the damper in fact closed. Diassembly of the zone motor from the drive shaft revealed a broken return spring on the shaft housing - not an internal spring on the drive motor such as a honeywell unit. My zone motors are an older ZONEX type. (2 wire/24 volt/60hz). Since i have isolated the problem, my questions are...
1. Is oxidation and fatigue the most likey culprit for the spring failure, or would the motor/controller have forcefully broken the spring by continuing to send a signal after fully opening the damper. (I believe the unit to be a power open/spring close unit) Oxidation is visible on the spring but not rust. It is very humid in Houston attics and the spring snapped at a tab bend - not in the coil - spring is in lower right of first picture...

2. Since the spring is external and has broken, will it be neccessary to replace the entire damper and shaft assembly and not just the motor? (For all I know the motor is still fine and has not burnt out.)

3. If just replaceing the motor with an internal spring unit, are any other modifications needed?

I cannot replace the motor with a 3 wire power open/power close unit without changing the controller. As a stop gap measure, I have coiled a wire coat hanger in the shaft assembly to keep the damper always open under static pressure. The bonus room is now cooling, however the unit was running slightly more requently due to the warm return air from the upstairs bonus room return. I have adjusted the thermostat for that zone to not call for service unless the temperature goes above 85 degrees. It seems to have stabilized around 83 degrees by only cooling when the downstairs themostat calls for service at 76 degrees.

Advertisement

Advice needed for zone damper repair...

clarification requested.
Since this motor unit had the spring external to the motor and installed in a notch on the shaft, replacing it with something like a honeywell motor with an internal spring will work?. I think i maybe confused because the shaft still has a piece installed with a small set screw that allowed me to wire the hanger in a slot to maintain an open damper blade.
My fear is that simply replacing the motor wont do anything to fix the problem because the external spring is broken.
So...
1. Are you saying that any replacement motor should come with an internal spring and that it would clamp on the naked damper shaft without the existing slotted shaft bushing? Pictures below show my current style motor on top, possible replacement on bottom...

2. Is it possible to just replace the spring? Is so, where the heck do i find one? I've looked everywhere...